A silver halide photographic light-sensitive material after image wise exposure forms the image in color by a color developing process wherein, in the exposed area, the oxidized product of an aromatic primary amine color developing agent reacts with a dye-forming coupler to produce a dye.
Generally in this photographic method, images in yellow, magenta and cyan are formed for reproducing the color images by substractive color reproduction method.
As couplers for producing images in color in the above-mentioned method, there are, for example, ones of the acylacetanilide type for yellow, ones of the types of pyrazolone, pyrazolobenzimidazol, pyrazolotriazol, and indazolone for magenta, and ones of the phenol and the naphthol types for cyan.
It is desired that the dye images obtained by the above-mentioned method do not discolor or fade when they are exposed to light for a long time or kept under high temperature or highly humid condition.
However, the fact is that the phenol-type and the naphthol-type couplers, on which the past studies for cyan dyes have centered, do not quite measure up to the expectations in respect of the spectral absorption characteristics, resistances to heat moisture, and the like of the cyan dye images produced.
On the other hand, for magenta, the use of 5-pyrazolone-based couplers, on which the studies have centered and which have been in wide use, are satisfactory in respect of the fastness of the dye images against heat and light, but the dye produced is lacking in pureness with an unwanted absorption of yellow as a component. To solve this problem, there have been proposals to use couplers of the types of pyrazolobenzimidazol, indazolone, pyrazolotriazol, imidazopyrazol, pyrazolopyrazol, pyrazolotetrazol, etc. Indeed the dyes produced by using these couplers are satisfactory in point of reproduction of color, but at the sacrifice of the fastness to light, which so retrogrades as to cause discoloration or fading.
In this connection U.S. Pat. No. 3,171,740 describes couplers consisting of compounds of the type of pyrazolo [1',5':3,2]-quinazolone, which indeed are satisfactory in respect of the spectral absorption characteristics, and the resistances to heat, moisture and light of the dye images produced. However, all of these couplers are of four equivalents, so that the development requires a relatively large quantity of silver halide, that is to say, to produce 1 mole of dye by reacting with the oxidized product of an aromatic primary amine color developing agent such a coupler theoretically requires 4 moles of silver halide to be developed.
As contrasted, a coupler of two equivalents requires only 2 moles of silver halide to be developed.
Furthermore, it has been found that photographic light-sensitive materials prepared by using the couplers in the description of the above-mentioned U.S. patent retrograde in photographic performance when made to stand in a hot, highly humid environment, this defect involving degradation of the sensitivity.
The research undertaken by the present inventors with the objective of solving the aforementioned problems has resulted in new two-equivalent couplers for forming photographic light-sensitive materials which are excellent in stability in storage and the dye images produced thereby are resistant to heat, moisture and light with respect to their influences on the hue.